Process of coating wood articles and articles produced thereby



Feb. 24, 1959 1E. F. KEMPEN 2,875,093

PROCESS OF 'ICOATING WOOD ARTICLES AND ARTICLES PRODUCED THEREBY Filed Nov. 4. 1954 2 SlietsSheet 1 FIGJ.

S W iv w f Feb. 24, 1959 E. F. KEMPEN 2,875,093

PROCESS OF COATING woon ARTICLES AND ARTICLES. PRODUCED TI-iEREBY Filed Nov. .4, 1954 FIG.4.

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v F Z V f l 3 M newrqz [mm/17f Kama-w Fri-viewe s PROCESS OF COATING WOOD ARTICLES AND ARTICLES PRODUCED THEREBY Edward F. Kempen, St. Louis, Mo., assignor to The Don- Ite Company, St. Louis, Mo., a corporation of Missouri Application November 4, 1954, Serial No. 466,847 5 Claims. (c1. 117-47 This invention relates to decorative and protective coatings, and more particularly to the manufacture of small articles requiring a fine finish, such as the heels of ladies shoes.

In explaining the invention, the heels of ladies shoes are taken as an example. Such an article necessarily must be capable of sustaining a load which may be considerable for its size, and it must have a finish which is tough and substantially free of defects. Conventionally, a wood block is turnedt'othe desired shape and sanded to a relatively smooth surface, but it is impractical, if not impossible, to sandout all of the tool marks, scratches and other indentations, at least to an extent such that a conventional finish coating may be applied.

Consequently, it has been necessary to resort to the procedure of applying a covering in sheet form. A blank of sheet material, such as nitrocellulose or cellulose acetate, is cut to size, softened and secured to the body, as by spot pasting at the margins. As the sheet hardens, it draws tight about the body, with the result that the underlying indentations in the body are substantially concealed, the outer surface thus being smooth. The attachment of such a sheet, however, requires considerable skill in order to prevent wrinkling, and the attachment is not too secure, because water may enterat the edges and attack the adhesive or wood. Being a manual operation, the process is also quite expensive.

Accordingly, there have been various efforts to sim plify the manufacture and reduce the cost of such heels. One of the proposals involved molding the entire heel from plastic material, but the selection of plastics is limited because they must not only be strong (in order to bear weight), but also tough and hard (so as to resist scufling). Also, the plastic-raw material is expensive, and since a typical heel factory may require as many as three hundred sizes. and styles, the die expense can approach prohibitive figures. With wood heels, this is not a major problem, because'the same woodturning machine can be utilized for manufacture of a wide variety of shapes merely by changing the cams and cutting implements'of the machine.

It is therefore an object of the present invention to provide. an improved process for manufacturing shoe heels and the like. More specifically, the invention includes among its objects the provision of a process for applying a durable decorative coating to a wood core, the wood core being the principalload-sustaining and shapedefining part of a heel; the provision of a process that may be carriedout substantially entirely with automatic machinery; the provision of a covering that is secured to the underlying wood body over the entire area and in such a .way as to conceal tool marks and other defects in the body; the provision of a process that permits handling of the heel up to a final spray coating without regard to the ultimate color of the heel; and the provision of a finish that resists peeling; chipping and abrasion.

In accordance with the present invention, briefly stated, a wood block is cutand rou h" sanded to the desired nited States atent 2,875,093 Patented Feb. 24, 9

shape using conventional machinery of a type known to those skilled in the art. As an initial step in the application of the finish, the article preferably is given a thin coat of sealer. This coating preferably is of a hot dip type so that air and moisture are driven from the wood while it is submerged within the hot sealer, the sealer then serving to close the pores of the wood. This sealer should be very thin and solvents would be used to achieve proper viscosity.

After the initial sealer has dried, at relatively thick intermediate coating is built up by dipping within a hot melt of thermoplastic material, but this hot melt should be substantially free of volatile solvent and wax. The hot melt contains a thermoplastic film-base, which is brought to a clipping viscosity of approximately seven thousand centipoises by melting within another resin of relatively greater fluidity. The hot melt may contain both soft and hard resins, but these components should not be used in amounts that would render the resulting film tacky and excessively soft or excessively brittle, respectively. j

According to the invention, an automatic dipping ma.- chine is to be employed for this purpose, such a machine having a conveyor upon which the heels are loaded. This conveyor preferably leads through a heating source which raises the temperature of the heels to that of the hot melt prior to dipping. After leaving the hot-melt, the heels are rotated to spread the hot melt evenly over the wood core, and theheels may then pass through a zone of reducing temperature, during which the plastic cools and solidifies.

Thereafter, the dip coated heels are sprayed witha pigmented lacquer about the side, back and breast walls to form a final coating which is relatively thin in comparison with the intermediate coating. Preferably, this final spray coating is applied Wet, or rather heavily, so as to substantially penetrate the intermediate coating. The invention contemplates, in one respect, that the final spray lacquer will include several solvents, one of which is a low boiler solvent for the base-of the lacquer only, and another of which is a relatively high boiler solvent for the intermediate coatings. As such, the final coating dries relatively quickly and tends to form a tight contracting film over the softened intermediate coating, thereby leveling the film and concealing imperfections, inthe surface of the woodwhich are not adequately hidden by the intermediate coating.

Other features of the invention will be in part apparent from and in part pointed out in the following detail description taken in connection with the accompanying drawings, in which:

Fig. 1 is an oblique view of a heel;

Fig. 2 is a detail sectional view of a heel in its finished condition, the thicknesses'of the coatings being exaggerated;

Fig. 3 is a simplified diagrammatic view of certain apparatus embodying the invention;

Fig. 4 is a section on the line 4-4 of Fig. 3, illustrating details of the apparatus; and v Fig. Sis a section taken on the line 55 of Fig. 4.

Referring now to Fig. l of the drawings, there is shown a wood core which has been shaped as a heel 1 for a ladys shoe. The upper portion 3 forming the seat of the heel may be concave and bears certain-size and style indicia, which is stamped or printed thereon. The opposite surface 5 is generally referred to as to the top, and the breast wall is designated 7. The side and back walls 9 and 11 are generally rounded as indicated;'

In manufacture, a tight grain wood, such as northern hard maple, is shaped on automatic wood cutting and sanding machinery, which is readilyadjusta'ble" sotha't different sizes and styles can be shaped on a standard machine. It should be understood, however, that while the wood is finished reasonably well, the surface is not sanded perfectly smooth, or at least to an extent such as would be satisfactory from a decorative point of view. Usually, there are imperfections in the grain and tool marks which must be consealed by the final finish.

Heretofore, such surface defects have been concealed beneath an overlying cover of Celluloid or other sheet covering material which is secured to the wood core, as by spot pasting. In the case of Celluloid, a sheet of suitable outline is softened and then tightly wrapped about the vertical surfaces 7, 9 and 11 of'the core, the edges of the sheet being brought together and secured by spot pasting over the breast wall 7. As the softened sheet dries, it tends to shring tightly about the wood core, with the result that a smooth flat decorative finish is provided. A core thus covered with Celluloid may then be sprayed with a light coating of lacquer of the desired color. It should be understood, however, that the Celluloid sheet is initially dye tinted, so that only a light spray coating of lacquer is needed for final finishing. A dye type of coloring is employed because a pigment would weaken the sheet, and the final spray coating is of a dusting nature, so that the solvent thereof does not deeply penetrate and soften the sheet of Celluloid.

The Celluloid sheet necessarily assures a smooth surface provided the sheet is properly applied, and the high tensile strength of Celluloid together with the substantial thickness of the sheet (ten-thousandths of an inch being a standard adopted by the industry) provides toughness. On the other hand, there are some disadvantages. The sheet is not secured to the wood core under its entire area and hence is subject to detachment, especially when water penetrates and attacks the adhesive. Also, the task of attaching the sheets to the core is a difficult manual operation; and it is generally necessary to use tinted sheets of varying color, depending upon the color of the final spray finish.

These objections are herein overcome by a process which involves dipping the core within a hot melt of thermoplastic film-forming material, thereby to provide a base or intermediate coating corresponding to the Celluloid sheet above described. This base coating preferably is clear to the extent that the size and style indicia on the seat 3 can be read, and the hot melt preferably is of a type such as to produce a coating of the desired thickness (approximately ten-thousandths of an inch) in a single dip.

Such a coating necessarily covers the entire Wood core, hence precludes entrance of moisture and is more firmly secured to the core. In order to improve the adhesion of this base coating, if desired, the wood core may initially be coated with a thin sealer 13. After application of the sealer, the core is dipped within the hot melt to form the base or intermediate coating 15, the resin setting to a hard film upon the withdrawal, and cooling of the heel. Thereafter, the vertical surfaces 7, 9, and 11 may be sprayed with a pigmented lacquer of desired color, so as to form a final coating 17. Such a lacquer would normally incorporate solvents that penetrate the base coating 15, the lacquer being sprayed sufiiciently heavy to provide adequate hiding power. I

The hot melt for the intermediate coating should be substantially free of volatile solvents and wax, a thermoplastic resin of good film-forming characteristics being broken down under heat to proper dipping viscosity. Al-

though viscosities as high as ten thousand centipoises are satisfactory, a viscosity of about seven thousand centipoises produces a film closer to the desired thickness.

It will be understood that certain thermoplastic materials have excellent film-forming properties but these materials are usually the most difficult to break down into homogeneous fluids. The viscosity may be reduced by means of volatile solvents, alone or in combination with heating, but such solvents are expensive and a considerable time is required for their evaporation. Also, when solvents alone are utilized to dissolve the filmforming components, they must be used in large quantities and the viscosity is accordingly low. Indeed, lacquers are generally too fluid to permit coating to desired thickness in a single dip.

On the other hand, those resins possessing the desired film-forming qualities cannot be broken down to dipping viscosity by heat alone. Where hot melt dipping has been practiced, as in the strip coating field, it has been customary to incorporate substantial amounts of wax, but such Waxes are not satisfactory for decorative purposes. Indeed, they produce waxy films which will not take an overlying spray finish. Also, the wax components tend to render the film soft and adhesive poor.

Among the thermoplastics recognized in the lacquer industry as possessing good film-formingproperties are nitrocellulose, cellulose acetate, cellulose acetate butyrate, ethyl cellulose, vinyl acetate, vinyl chloride, vinyl acetatechloride, polystryene, and the acrylic resins. The alkyd and maleic resins are not generally satisfactory as the sole constituent of a coating, since they lack strength, but they are frequently used in combination, particularly with the cellulose esters to improve gloss. For purposes of this invention, nitrocellulose and cellulose acetate may be excluded because of their narrow operating range between melting and decomposition temperature. The acrylic resins are satisfactory but for their expense, and polystryene tends to behave poorly when sprayed with a lacquer. Therefore, cellulose acetate butyrate and ethyl cellulose are suggested as the most suitable film-forming components for the hot melt, although the vinyl resins may be used, especially-when a rubbery film is desired, as might be the case in coating wedge shoe heels.

The hot melt should be maintained at a high temperature in order to achieve an adequately fluid melt, but decomposition results when the temperature is excessive. For this reason, a temperature of 350 F. is suggested as practical value.

The suggested film-forming constituents, however, cannot be sufficiently plasticized by heat alone, hence dipping viscosity is achieved by admixing other resins that are relatively more fluid at the temperature of the hot melt. At a temperature of 350 F., many resins (notably those lacking good film-forming qualities) are quite fluid in comparison to those possessing such properties. These materials may be broadly classified into hard resins (which are solids at a normal temperature of say 70 F.) and soft resins (which vary from liquids to soft sticky resins at a normalv temperature). The soft resins, in turn, might be subdivided into those which are nonvolatile solvents for the film-forming constituent and those that do not have a solvent action, but are comparable to the volatile diluents in lacquers as regards solvent action. In all cases, the resinsadd'ed to the cellulose ester should be compatible in the quantities used, however. In other words, the resin should not crystallize upon cooling so as to produce a cloudy film.

It may be noted that the soft resins also plasticize the resulting film as well as the hot melt, and hence cannot be used in unlimited quantities, if the film is not to be soft and tacky. A limited amount of plasticizing action is desirable, however, especially with the cellulose esters, because the resistance to cold check is thereby improved. On the other hand, the hard resins improve gloss and harden the film.

Accordingly, the base of the hot melt may be one of the cellulose or vinyl esters that has a working difference between its melting and decomposition temperature, this constituent serving to provide film strength. ..Dipping viscosity is achieved by melting the base in one or more compatible thermoplastics having acomparatively low viscosityat thetemperature of the hot melt (350 F.),

but the plasticizing constituents must not produce an overplasticizing film at a normal temperature (70 F.). Breakdown of the film base is facilitated by use of a solvent-type plasticizer, additional thinning action being had from non-solvent hard and soft resins, which have a relatively low viscosity when heated.

For example, a satisfactory mixture might be made as follows:

Percent by weight as Aroclor 5460 In the above example, the cellulose acetate butyrate is the film base, and the dioctal phthalate is a soft resin solvent-type plasticizer for the cellulose base. The chlorinated biphenyls range from viscous oils to crystalline powders and hard resins, the crystalline form occurring when the chlorine content reaches 68% and stable noncrystalline solid states being achieved (at normal temperature) by admixing varying percentages of high-boiling polyphenyls, which raise the softening point of the chlorinated biphenyl mixture. In the example given, the chlorinated biphenyl of 60% chlorine content is a soft sticky resin, whereas the chlorinated terphenyl is a hard resin.

It should be understood, however, that the several components of the hot melt may be varied in amount and in type. For example, ethyl cellulose might be employed in place of cellulose acetate 'butyrate. Another suitable solvent-type plasticizer would #be tricresyl phosphate. Other suitable hard resins include a medium oil alkyd resin containing 33% phthalic anhydride and 55% dehydrated castor oil (Duraplex C55) and a rosin modified short oil alkyd resin containing 35% phthalic. anhydride and dehydrated castor oil (France, Campbell and Darling 555). Another soft resin of the non-solvent type would be hydrogenated methyl abietate (Hercolyn).

In other words, the film base is broken down to dipping viscosity by the use of non-volatile waxless thermoplastic resins' that (1) have a relatively low viscosity at the temperature of the hot melt, (2) do not decompose or distill off at the temperature of the hot melt, (3) are compatible with the base in the quantities used, and (4) do not overplasticize the film in the quantities used. Al- I though only one such resin may be employed, a combination is preferred. If hard' resin alone is utilized, the film has high gloss, but tends to be weak and brittle. If soft resins are the soleconstituent with the base, the film is flexible but tends to be soft and tacky.

In forming the initial sealing coat, a conventional lacquer sealer may be utilized although it is preferable to employ a hot-dip type of sealer. A satisfactory hot resin sealer could be made with a solids content of 75% maleic resin and lacquer-grade ethyl cellulose. The solvent could be 90% toluol and 10% butyl alcohol, the solids being 20% of the solution and the mixture being heated to about 150 F. in a jacketed tank so as to produce a thin solution. The heels are held in the tank until bubbling ceases. It may be noted that such a hot resin sealer is especially desirable since the film tends to remain hard in the subsequent hot melt dip. Although the hot sealer is fluid at a temperature of 150 F., the resulting film has a higher melting point because of evaporation of the solvents.

The final coating would be applied as a lacquer from a spray gun, any conventional lacquer being suitable, provided it is compatible with the intermediate coating. In most instances, the intermediate coating will be colorless and the final coating will contain pigments for producing the desired color. This procedure is desirable from a manufacturing point-0f view inasmuch as all the heels may be dip coated within the same hot melt. Where a large number of heels are to 'be of the same color, however, as in the case of black heels, the coloring pigment might be incorporated in the hot melt for the intermediate coating, but this procedure necessarily results in blacking out the size and-style'indicia.

Whereas conventional spray lacquers may be employed, it is preferable to utilize a lacquer having certain contracting characteristics, because some of the surface irregularities of the wood may not be entirely hidden by the intermediatecoating. In that event, it is desirable to utilize spray lacquer which will penetrate'and in part soften-the intermediate coating, the spray lacquer including a solvent mixture which skins over upon evaporation of the low-boiler solvents.

For example, the final spray lacquer could be made with a solid content by weight of 25% pigments, 15% cellulose acetate, 25 nitrocellulose .(high viscosity type, such as five second or one-half secondviscosity), 25% plasticizer and 10% hard resin. The plasticizer might be methyl phthalyl. ethyl glycolate (Santicizer M-17) or chlorinated biphenyl of 54% combined chlorine by weight '(Aroclor 1254) and the hard resin would be of a type compatible with the cellulose acetate and nitrocellulose, such as chlorinated biphenyl' of 60% combined chlorine by weight (Aroclor 1260.). A thinnerfor the above might be made up from 10% ethyl lactate, 30% acetone, 40% methyl Cellosolv'e, 10% alcohol, and 10% toluol.-

The acetone is a low boiler solvent for'the cellulose acetate and evaporates quickly, so that the cellulose acetate dries rapidly and skins over while the underlying film remains soft. Such an underplasticized film produces a tauteningaction, and since the other relatively-high boiler substances do not resoften the skins, the softened underlying portions of the filmare leveled. In other words, the solvents control the tautening' effect, the adjustment being such that the coating does not pull or separate at the edges, yet is suflicient to provide for leveling of the finish. Necessarily, the solvents should in part penetrate and soften the intermediate coating, when the intermediate coating is to be leveled with a spray lacquer of this character.

Referring now to Fig. 3 of the drawings, there is shown certain apparatus which might be employed in connection with the intermediate dip-coating step of the process. Such apparatus might include a pair of opposed endless conveyors 21 trained about sprockets 23 at the sides of the machine. The conveyors 21 lead along a vertical path at one end of the machine, which forms a-zone-L for loading and unloading the machine. The conveyors are driven in a direction indicated by the arrows, so that articles carried thereby, in leaving the loading zone L, pass into a: primary heat zone PH, which may be enclosed at 25 and have suitable heating devices 27, such as infrared lamps. The heating zone H then leads directly to a dip tank T, and the articles are carried from the tank through a second heating zone SH. Finally, the articles pass from the heat zone to a final cooling Zone C, and from there to the loading zone L.

The dip'tank T is shaped as a trough, which is partitioned transversely by a plurality of heating elements 29,

thereby to provide a plurality of dipping compartments 31. Each dipping compartment is of a width sufficient to accommodate a heel and of a length (the tank being of a width) such as to permit immersion of the heels as the conveyor moves thereby.

Referring to Figs. 4 and 5, the article-carrying conveyors may be constituted by endless chains 21 which travel along fixed guides 33. Rods 35 extend between and are carried by the chains, these rods being removablyjournalled in bearings 37, which are attached to the chains. The rods 35, in turn, carry spikes 39, which project radially at suitably spaced intervals therealong.-

"7 Each rod 35 may have as many as ten sets of spikes, each set consisting of four spikes, so that a given rod may normally carry forty heels impaled upon the spikes. The rods are loosely held by the bearings, so that they may be readily loaded onto and removed from the machine at the loading zone L by insertion in an axial direction.

In addition, shives or sprockets 41 are affixed to the ends of the rods for cooperation with fixed rails 43, the arrangement being one such as to rotate the rods when the shives 41 engage the rails 43. The rails extend over the tank T and through the heating and cooling zones PH, SH and C. The articles are thus rotated as they enter, pass through and emerge from the dip tank, such rotation being continued as the thermoplastic coating cools and solidifies on the heels.

The initial heating zone PH heats the wood cores 1 to a temperature approximately the same as that of the hot melt thermoplastic in the tank T, the latter being heated by the heating elements 29. The second heating zone SH is designed to maintain the cores at the temperature of the hot melt bath as they emerge therefrom for a short distance (for example, an amount sufiicient to provide one complete revolution of a heel) and then to gradually reduce the temperature as the heels are slowly rotated or upended, so that the coating flows back and forth as it gradually cools and solidifies.

It may be noted that the conveyor extends along a path immediately above the top surface of the hot melt, so that spikes on the rods may dip into the hot melt. This path is of a length sufficient to provide for a complete revolution and immersion of all four heels as a rod 35 traverses the dipping zone.

In normal operation, a rod 35 would be unloaded at the bottom of the zone L, and a fresh rod would be loaded onto the machine at the top of this zone. These rods may be stacked upon racks, but normally, the heels would immediately be removed from the spikes and transferred to the spray-finishing station. At the sprayfinishing station, a heel may be mounted on a holder and rotated about a vertical axis, so that the surfaces 5 and 9 thereof are swept past a relatively fixed spray gun.

From the foregoing description, it is apparent that those skilled in the art will understand the structure, function and mode of operation of the invention herein disclosed, and appreciate the advantages thereof. Although one embodiment has been disclosed in detail, it is to be understood that the invention is not limited thereto, but the drawings and description thereof are to be understood as being merely illustrative. It is realized that many modifications and variations will present themselves to those skilled in the art without departing from the spirit of this invention or the scope thereof as set forth in the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. In'the process of coating shoe heels and the like, the steps of dipping the article in a hot melt consisting essentially of non-waxy, non-volatile thermoplastic resins that produce a film upon cooling to normal temperatures of about F., and then spraying the article with a lacquer so as to provide a final coat relatively thin in comparison with said first coat, said lacquer having a leveling effect upon the first coat.

2. The process set forth in claim 1, wherein the lacquer contains solvents, one of which is a low-boiler solvent having a relatively low solvent action on the first coating and another of which is a high-boiler solvent having relatively high solvent action on the first coating, both of said solvent constituents having relatively high solvent action on the base of the lacquer.

3. A process of providing a relatively thick protective coating for wood articles such as shoe heels and the like, which comprises the steps of applying a relatively thin primer coat of resinous material, then dipping the article in a hot melt of non-pigmented non-waxy thermoplastic resins to produce a coat of about ten thousandths of an inch in thickness, and then applying a relatively thin final coat of pigmented lacquer.

4. A wood article of the character disclosed having a protective decorative covering comprising a relatively thick intermediate coat of ethyl cellulose sandwiched between two relatively thin coats, the thickness of the intermediate coat being a least about ten thousandths of an inch, and the thin outermost coat being a nitrocellulose lacquer.

5. A wood article of the character disclosed having a protective decorative covering comprising a relatively thick intermediate coat of ethyl cellulose sandwiched between two relatively thin' coats, the intermediate coat having a thickness of at least ten thousandths of an inch and being clear, and the thin outermost coat being the pigmented nitrocellulose lacquer.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE PROCESS OF COATING SHOE HEELS AND THE LIKE, THE STEPS OF DIPPING THE ARTICLE IN A HOT MELT CONSISTING ESSENTIALLY OF NON-WAXY, NON-VOLATILE THERMOPLASTIC RESINS THAT PRODUCE A FILM UPON COOLING TO NORMAL TEMPERATURES OF ABOUT 70* F., AND THEN SPRAYING THE ARTICLE WITH A LACQUER SO AS TO PROVIDE A FINAL COAT RELATIVELY THIN IN COMPARISON WITH SAID FIRST COAT, SAID LAQUER HAVING A LEVELING EFFECT UPON THE FIRST COAT. 